Field of Invention
Various embodiments of the present disclosure relate to a multi-channel receiver optical sub-assembly and a manufacturing method thereof.
Description of Related Art
As broadband mobiles, clouding networks, IPTVs and smart-phones are spreaded, video-based high-capacity communications are explosively increased. Thus, a transmission rate of an optical module is dramatically increased, and simultaneously, there is an urgent need for technology that may implement a receiver optical sub-assembly in a very small size and at a low cost.
Generally, when the receiver optical sub-assembly uses an AWG (Arrayed Waveguide Grating) PLC (Planar Lightwave Circuit) chip having a function of wavelength multiplexing filter, or a PLC chip on which a multi-channel straight waveguide is formed, first, one end of the PLC chip is vertically 90° polished so as to implement a light receiving part on one end of the PLC chip. Subsequently, an SI-PD (Surface-Illuminated Photo Diode) on which the lens is not integrated is precisely flip-chip bonded to a top of a PD (Photo Diode) carrier.
Therefore, in order to effectively couple an optical signal outputted from the PLC chip with the SI-PD, the PLC chip that is vertically polished at one end thereof and the PD carrier on which the SI-PD is integrated are arranged to face each other. In this state, a bulky glass lens is inserted between the PLC chip and the SI-PD so that the PLC chip and the SI-PD are horizontally arranged. Thereafter, active alignment and butt-coupling should be performed between the PLC chip and the SI-PD.
In the case of an SI-PD for optical communication of 25 Gbps or more, the diameter of a light receiving part of the SI-PD is very small, that is, about 20 um, so that it is very difficult to passively align the SI-PD with the PLC chip. That is, in the case where the SI-PD, the glass lens, and the PLC chip are discretely passively aligned with each other, if the misalignment of about 10 um occurs for the narrow light receiving part of the SI-PD, optical coupling efficiency between the SI-PD and the PLC chip is remarkably lowered. Therefore, the PLC and the SI-PD should be actively aligned with each other.
Accordingly, if the PLC chip and the SI-PD are actively aligned with each other, the lens is disposed between the SI-PD and the PLC chip as described above, so as to enhance optical coupling efficiency and a yield. In this respect, since the conventional light receiving part should use a glass lens with a large size, the length of the light receiving part is increased. Further, after the PLC chip, the lens, and the SI-PD are discretely arranged, they should be actively aligned and assembled with each other. Thus, a process is complicated and a long time is required, so that it is difficult to achieve a reduction in cost of the receiver optical sub-assembly.
In the conventional receiver optical sub-assembly, the SI-PD is disposed on a side of the PD carrier, and a TIA array amplifying a photo-current, outputted from the SI-PD, to a high voltage is disposed on a top of the PD carrier. Therefore, a high frequency transmission line between the SI-PD and the TIA array is bent at 90°. At this time, if a high speed signal of 25 Gbps or more passes through the high frequency transmission line that is bent at 90°, severe impedance mismatch occurs and a high frequency signal is radiated, so that the performance of the receiver optical sub-assembly is considerably deteriorated.
Consequently, in the related art, when the receiver optical sub-assembly of 25 Gbps or more is mass-produced, production yield is reduced in terms of high frequency characteristics, thus making it very difficult to achieve a reduction in cost of the receiver optical sub-assembly. Particularly, in a receiver optical sub-assembly of 40 Gbps or more, deterioration in high frequency characteristics becomes more serious. Therefore, in the related art, another structure should be applied to the receiver optical sub-assembly of 40 Gbps or more. As a result, it is impossible to use the conventional receiver optical sub-assembly as a universal structure of a receiver optical sub-assembly for a high frequency.